OF-857: Synchronize connection/session cleanup

This patch is to prevent a stack overflow in certain exception cases
where a connection has been closed, but its corresponding session is
still present in the routing table.

src/java/org/jivesoftware/openfire/nio/NIOConnection.java

@@ -203,25 +203,22 @@ public class NIOConnection implements Connection {
     }
 
     public void close() {
-        boolean closedSuccessfully = false;
-        synchronized (this) {
-            if (!isClosed()) {
-                try {
-                    deliverRawText(flashClient ? "</flash:stream>" : "</stream:stream>", false);
-                } catch (Exception e) {
-                    // Ignore
-                }
-                if (session != null) {
-                    session.setStatus(Session.STATUS_CLOSED);
-                }
-                ioSession.close(false);
-                closed = true;
-                closedSuccessfully = true;
+    	synchronized(this) {
+    		if (isClosed()) {
+    			return;
+    		}
+            try {
+                deliverRawText(flashClient ? "</flash:stream>" : "</stream:stream>", false);
+            } catch (Exception e) {
+                // Ignore
             }
-        }
-        if (closedSuccessfully) {
-            notifyCloseListeners();
-        }
+            if (session != null) {
+                session.setStatus(Session.STATUS_CLOSED);
+            }
+            notifyCloseListeners(); // clean up session, etc.
+            closed = true;
+    	}
+        ioSession.close(false); // async via MINA
     }
 
     public void systemShutdown() {
@@ -248,11 +245,8 @@ public class NIOConnection implements Connection {
         session = owner;
     }
 
-    public boolean isClosed() {
-        if (session == null) {
-            return closed;
-        }
-        return session.getStatus() == Session.STATUS_CLOSED;
+    public synchronized boolean isClosed() {
+        return closed;
     }
 
     public boolean isSecure() {